As the extended deadline for the Google book settlement approaches, agents, authors, and other industry professionals still disagree about how the massive book-scanning project will affect authors. After William Morris Endeavor, one of the country’s largest agencies, issued a memo last week advising its clients to opt out of the deal, the Authors Guild, which supports the settlement, released a rebuttal on Monday. The Guild will host an open conference call tomorrow afternoon to address what it calls “a series of erroneous conclusions” drawn by the agency.

According to a memo obtained by the New York Times, William Morris urged its authors to reject the settlement because it would “bind copyright owners in any book published prior to January 9, 2009 to its terms.” An attorney for the agency told the Times that the $125 million arrangement would give Google the right to sell books “at a pre-negotiated one-time royalty,” saying the deal was “like a legislative change” that authors could only hope to alter by heading back to the courts.

In an e-mail sent to Authors Guild members on Monday, the advocacy group claimed William Morris had misjudged the rigidity of the settlement, saying the only right waived by authors who opt in is the right to sue Google. The Guild wrote that under the terms of the arrangement copyright holders would retain the power to terminate any of the rights granted to Google to scan, display, and sell books. “There’s plenty of time to exercise all of your rights and benefits under the settlement,” the Guild wrote, “including the right to say ‘no’ to any and all uses—after the settlement’s approved.”

The 334-page settlement is the product of an agreement reached last October between the Authors Guild and Google. The Internet giant, which operates an extensive book-scanning project, had been the target of a class action copyright infringement suit brought on behalf of authors and publishers. In April, the deadline for authors to accept or reject the settlement was extended to September 7.

The Authors Guild’s conference call is scheduled for three o’clock EST. Authors can sign up for the free call here.